Gauss type photographic lens

ABSTRACT

A Gauss type photographic lens comprises, in succession from the object side, a first group including a positive lens component, a second group including a positive lens and a negative lens and having a negative refractive power as a whole, a third group including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group including a positive lens component. The lens component in said fourth group is movable along the optical axis and the focusing is accomplished only by movement of said movable lens.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a Gauss type photographic lens, and particularly to improvements in the focusing system thereof.

2. Description of the Prior Art

Generally, the focusing of a photographic lens is accomplished by the so-called whole axial movement system which requires the movement of the whole lens system. However, according to this system, the whole lens system, which is a mass of great weight, is moved. This has led to a complex and bulky construction of the lens barrel and also to difficulties both in portability and operability.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a Gauss type photographic lens the focusing of which can be accomplished by a simple construction.

The present invention relates to a Gauss type photographic lens comprising, in succession from the object side, a first group G₁ including a positive lens component, a second group G₂ including a positive lens and a negative lens and having a negative refractive power as a whole, a third group G₃ including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group G₄ including a positive lens component, wherein some or all of the lens components in the fourth group are movable along the optical axis and focusing is accomplished only by this movable lens.

The invention will become fully apparent from the following detailed description thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a), 2(a) and 3(a) show the lens arrangements according to a first, a second and a third embodiment of the present invention.

FIGS. 1(b), 2(b) and 3(b) illustrate the various aberrations in the respective embodiments with respect to an object at infinity.

FIGS. 1(c), 2(c) and 3(c) illustrate the various aberrations in the respective embodiments with respect to an object at a short distance (β=-1/40).

FIGS. 2(d) and 3(d) illustrate the various aberrations in the second and third embodiments with respect to an object at a short distance (β=-1/40) in the case of another focusing system according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A first embodiment of the present invention shown in FIG. 1(a) will hereinafter be described. The construction of the lens according to the present embodiment is what is known as a typical Gauss type photographic lens. In succession from the object side, a first group G₁ thereof is a positive lens component having its surface of sharper curvature facing the object side, a second group G₂ thereof is a negative meniscus lens component comprising a positive lens and a negative lens cemented together and having its convex surface facing the object side, a third group G₃ thereof is a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group G₄ is a biconvex positive lens component. A diaphragm is provided between the second group and the third group. In such a lens construction, according to the present invention, the first group G₁, the second group G₂ and the third group G₃ are always fixed irrespective of the object distance, namely, irrespective of the photographing magnification, and the fourth group G₄ is movable along the optical axis so that focusing is accomplished by the movement of only the fourth group G₄. Specifically, during focusing to an object at inifinity, the air space between the third group G₃ and the fourth group G₄ is greatest and as the lens is focused to a short distance and the fourth group G₄ is moved toward the object side so that said air space becomes smaller. When the influence of the variable space between the third group G₃ and the fourth group G₄ upon aberrations is considered, it is desirable that the total focal length fa of the fixed first, second and third groups be in the range of fa>2.0 f, where f is the total focal length of the entire system. The various aberrations in the present embodiment when focused to infinity are shown in FIG. 1B, and the various aberrations when focused to a short distance, for example in the case of a photographing magnification β=-1/40, are shown in FIG. 1C.

A second embodiment of the present invention, as shown in the lens arrangement of FIG. 2A, is substantially identical to the above-described first embodiment in the construction of the first group G₁ to the third group G₃, but the positive lens component of the fourth group G₄ is divided into a biconvex positive lens component and a positive meniscus lens component having its convex surface facing the image side. Focusing may be accomplished by the integral movement of both the positive lens component and the positive meniscus lens component. In this case, it is desirable that the total focal length fa of the first group G₁ to the third group G₃ should be fa>1.5f. The various aberrations in the present embodiment when focused to infinity are shown in FIG. 2B, and the various aberrations when focused to a short distance, for example in the case of a photographing magnification β=-1/40, are shown in FIG. 2C.

In the present embodiment, focusing can also be accomplished by moving only the biconvex positive lens component in the fourth group G₄. This is a kind of internal focusing system and, in order to reduce the amount of movement of this movable biconvex positive lens component to thereby make the entire system more compact, it is desirable that the total focal length fb of the first group G₁ to this positive lens component during focusing to infinity should be in the range of f>fb>f. The various aberrations for the photographing magnification β=-1/40 in this case are shown in FIG. 2D.

A third embodiment of the present invention, as shown in the lens arrangement of FIG. 3A, is substantially identical to the above-described first and second embodiments except for the construction of the fourth group. In the present embodiment, the single positive lens component which is the fourth group in the first embodiment is divided into a biconvex positive lens component and a negative meniscus lens component having its convex surface facing the image side and the focusing is accomplished by moving these two lens components together. In this case, it will suffice if the composite refractive power of the fourth group is only positive, but from the viewpoint of aberrations, it is desirable that the total focal length fa of the first group G₁ to the third group G₃ be fa>2.0f. The various aberations in the present embodiment when focusing to infinity, and in the case of a photographing magnification β=-1/40 are shown in FIGS. 3(b) and 3(c), respectively.

Again in the present embodiment, focusing can also be accomplished by movement of only the biconvex positive lens component in the fourth group G₄. In this case, it is desirable that the total focal length fb of the first group G₁ to this movable positive lens component during focusing to infinity should be in the range of 0.6 f>fb>f, so that the fluctuation of spherical aberration resulting from focusing can be better corrected. The various aberrations for the photographing magnification β=-1/40 in this case are shown in FIG. 3(d).

Numerical data of the various embodiments of the present invention will be shown below. In the tables below, R represents the radius of curvature of each lens surface, d represents the spacing between adjacent lens surfaces, nd and νd represent the refractive index and Abbe number, respectively, of each lens, and the subscript numbers represent the order from the object side, and fa and fb are as defined above.

    ______________________________________                                         First Embodiment                                                               Total focal length f = 100.0, F-number 2.5,                                    Angle of view 30°                                                       ______________________________________                                         R.sub.1 = 65.13                                                                          d.sub.1 = 5.5                                                                             nd.sub.1 = 1.7481                                                                           νd.sub.1 = 52.3                           R.sub.2 = 165.0                                                                          d.sub.2 = 0.13                                                       R.sub.3 = 37.25                                                                          d.sub.3 = 12.5                                                                            nd.sub.2 = 1.67025                                                                          νd.sub.2 = 57.5                           R.sub.4 = 575.0                                                                          d.sub.4 = 7.25                                                                            nd.sub.3 = 1.61293                                                                          νd.sub.3 = 36.9                           R.sub.5 = 23.13                                                                          d.sub.5 = 25.75                                                      R.sub.6 = -28.63                                                                         d.sub.6 = 1.88                                                                            nd.sub.4 = 1.75692                                                                          νd.sub.4 = 31.7                           R.sub.7 = 312.5                                                                          d.sub.7 = 8.38                                                                            nd.sub.5 = 1.744                                                                            νd.sub.5 = 44.9                           R.sub.8 = -38.88                                                                         d.sub.8 = 11.0                                                       R.sub.9 = 218.75                                                                         d.sub.9 = 5.63                                                                            nd.sub. 6 = 1.79668                                                                         νd.sub.6 = 45.4                           R.sub.10 = -85.08                                                              Back focal length Bf = 48.35                                                   ______________________________________                                    

The variable space d₈ =8.16 for the photographing magnification β=-1/40.

fa=272.9

    ______________________________________                                         Second Embodiment                                                              Total focal length f = 100.0, F-number 2.2,                                    Angle of view 26°                                                       ______________________________________                                         R.sub.1 = 65.25                                                                          d.sub.1 = 5.5                                                                             nd.sub.1 = 1.7481                                                                           νd.sub.1 = 52.3                           R.sub.2 = 165.0                                                                          d.sub.2 = 0.13                                                       R.sub.3 = 37.25                                                                          d.sub.3 = 12.5                                                                            nd.sub.2 = 1.67025                                                                          νd.sub.2 = 57.5                           R.sub.4 = 625.0                                                                          d.sub.4 = 7.25                                                                            nd.sub.3 = 1.61293                                                                          νd.sub.3 = 36.9                           R.sub.5 = 23.0                                                                           d.sub.5 = 25.63                                                      R.sub.6 = -28.85                                                                         d.sub.6 = 1.25                                                                            nd.sub.4 = 1.75692                                                                          νd.sub.4 = 31.7                           R.sub.7 = 312.5                                                                          d.sub.7 = 8.25                                                                            nd.sub.5 = 1.744                                                                            νd.sub.5 = 44.9                           R.sub.8 = -39.0                                                                          d.sub.8 = 10.0                                                       R.sub.9 = 275.0                                                                          d.sub.9 = 5.0                                                                             nd.sub. 6 = 1.79668                                                                         νd.sub.6 = 45.4                           R.sub.10 = -112.5                                                                        d.sub.10 = 0.25                                                      R.sub.11 = -125.0                                                                        d.sub.11 = 3.75                                                                           nd.sub.7 = 1.744                                                                            νd.sub.7 = 44.9                           R.sub.12 = -80.52                                                              Back focal length Bf = 47.83                                                   ______________________________________                                    

The variable space d₈ =7.18 for a photographing magnification β=-1/40.

(In the case of the focusing by only biconvex positive lens component in the fourth group, the variables spaces d₈ and d₁₀ are d₈ =5.89 and d₁₀ =4.36 for β=-1/40.)

fa=282.15

fb=117.68

    ______________________________________                                         Third Embodiment                                                               Total focal length f = 100.0, F-number 2.2,                                    Angle of view 26°                                                       ______________________________________                                         R.sub.1 = 65.25                                                                          d.sub.1 = 5.5                                                                             nd.sub.1 = 1.7481                                                                           νd.sub.1 = 52.3                           R.sub.2 = 165.0                                                                          d.sub.2 = 0.13                                                       R.sub.3 = 37.25                                                                          d.sub.3 = 12.5                                                                            nd.sub.2 = 1.67025                                                                          νd.sub.2 = 57.5                           R.sub.4 = 625.0                                                                          d.sub.4 = 7.25                                                                            nd.sub.3 = 1.61293                                                                          νd.sub.3 = 36.9                           R.sub.5 = 23.125                                                                         d.sub.5 = 25.88                                                      R.sub.6 = -28.88                                                                         d.sub.6 = 1.63                                                                            nd.sub.4 = 1.75692                                                                          νd.sub.4 = 31.7                           R.sub.7 = 312.5                                                                          d.sub.7 = 8.38                                                                            nd.sub.5 = 1.744                                                                            νd.sub.5 = 44.9                           R.sub.8 = -39.19                                                                         d.sub.8 = 10.00                                                      R.sub.9 = 218.75                                                                         d.sub.9 = 6.88                                                                            nd.sub. 6 = 1.79668                                                                         νd.sub.6 = 45.4                           R.sub.10 = -68.75                                                                        d.sub.10 = 0.25                                                      R.sub.11 = -68.75                                                                        d.sub.11 = 1.88                                                                           nd.sub.7 = 1.79668                                                                          νd.sub.7 = 45.4                           R.sub.12 = -83.75                                                              Back focal length Bf = 47.25                                                   ______________________________________                                    

The variable space d₈ =7.16 for a photographing magnification β=-1/40.

(In the case of the focusing by only the biconvex positive lens component in the fourth group, the variable spaces d₈ and d₁₀ are d₈ =7.73 and d₁₀ =2.52 for ⊖=-1/40.)

fa=274.3

fb=90.5

According to the present invention as described above, the movement of the lens for focusing is effected only in the fourth group that is most adjacent to the image side and, therefore, focusing can be accomplished by a simple construction and the various interlocking mechanisms with the camera body are simplified, thus enhancing the operability to a higher degree.

The present invention is applicable not only to the above-described typical Gauss type photographic lens but also to a so-called modified Gauss type photographic lens in which the positive lens and the negative lens in the second group are separated from each other, and can provide a photographic lens of greater aperture ratio. 

I claim:
 1. A Gauss type photographic lens comprising, in succession from the object side, a first group including a positive lens component, a second group including a positive lens and a negative lens and having a negative refractive power as a whole, a third group including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group including a positive lens component comprising a biconvex positive lens and a negative meniscus lens having its convex surface facing the image side, focusing being effected by movement along the optical axis of either both said biconvex positive lens and said negative meniscus lens or by movement of only said biconvex positive lens.
 2. A Gauss type photographic lens comprising, in succession from the object side, a first group including a positive lens component, a second group including a positive lens and a negative lens and having a negative refractive power as a whole, a third group including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group including a positive lens component movable along the optical axis, focusing being accomplished only by movement of said movable positive lens component, and wherein numerical data are as follows:

    ______________________________________                                         Total focal length f = 100.0, F-number 2.5,                                    Angle of view 30°                                                       ______________________________________                                         R.sub.1 = 65.13                                                                          d.sub.1 = 5.5                                                                             nd.sub.1 = 1.7481                                                                           νd.sub.1 = 52.3                           R.sub.2 = 165.0                                                                          d.sub.2 = 0.13                                                       R.sub.3 = 37.25                                                                          d.sub.3 = 12.5                                                                            nd.sub.2 = 1.67025                                                                          νd.sub.2 = 57.5                           R.sub.4 = 575.0                                                                          d.sub.4 = 7.25                                                                            nd.sub.3 = 1.61293                                                                          νd.sub.3 = 36.9                           R.sub.5 = 23.13                                                                          d.sub.5 = 25.75                                                      R.sub.6 = -28.63                                                                         d.sub.6 = 1.88                                                                            nd.sub.4 = 1.75692                                                                          νd.sub.4 = 31.7                           R.sub.7 = 312.5                                                                          d.sub.7 = 8.38                                                                            nd.sub.5 = 1.744                                                                            νd.sub.5 = 44.9                           R.sub.8 = -38.88                                                                         d.sub.8 = 11.0                                                       R.sub.9 = 218.75                                                                         d.sub.9 = 5.63                                                                            nd.sub.6  = 1.79668                                                                         νd.sub.6 = 45.4                           R.sub.10 = -85.08                                                              Back focal length Bf = 48.35                                                   fa = 272.9                                                                     ______________________________________                                    

wherein d₈ is a variable space and d₈ =8.16 for a photographing magnification β=-1/40, and wherein R represents the radius of curvature of each lens surface, d represents the spacing between adjacent lens surfaces, nd and νd represent the refractive index and Abbe number, respectively, of each lens, the subscript numbers represent the order from the object side, and fa represents the focal length of the first, second and third groups.
 3. A Gauss type photographic lens comprising, in succession from the object side, a first group including a positive lens component, a second group including a positive lens and a negative lens and having a negative refractive power as a whole, a third group including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group including a movable positive lens component comprising a biconvex positive lens and a positive meniscus lens having its convex surface facing the image side, focusing being effected by movement along the optical axis of either both said biconvex positive lens and said positive meniscus lens or by movement of only said biconvex positive lens, and wherein numerical data are as follows:

    ______________________________________                                         Total focal length f = 100.0, F-number 2.2,                                    Angle of view 26°                                                       ______________________________________                                         R.sub.1 = 65.25                                                                          d.sub.1 = 5.5                                                                             nd.sub.1 = 1.7481                                                                           νd.sub.1 = 52.3                           R.sub.2 = 165.0                                                                          d.sub.2 = 0.13                                                       R.sub.3 = 37.25                                                                          d.sub.3 = 12.5                                                                            nd.sub.2 = 1.67025                                                                          νd.sub.2 = 57.5                           R.sub.4 = 625.0                                                                          d.sub.4 = 7.25                                                                            nd.sub.3 = 1.61293                                                                          νd.sub.3 = 36.9                           R.sub.5 = 23.0                                                                           d.sub.5 = 25.63                                                      R.sub.6 = -28.85                                                                         d.sub.6 = 1.25                                                                            nd.sub.4 = 1.75692                                                                          νd.sub.4 = 31.7                           R.sub.7 = 312.5                                                                          d.sub.7 = 8.25                                                                            nd.sub.5 = 1.744                                                                            νd.sub.5 = 44.9                           R.sub.8 = -39.0                                                                          d.sub.8 = 10.0                                                       R.sub.9 = 275.0                                                                          d.sub.9 = 5.0                                                                             nd.sub.6  = 1.79668                                                                         νd.sub.6 = 45.4                           R.sub.10 = 112.5                                                                         d.sub.10 = 0.25                                                      R.sub.11 = -125.0                                                                        d.sub.11 = 3.75                                                                           nd.sub.7 = 1.744                                                                            νd.sub.7 = 44.9                           R.sub.12 = -80.52                                                              Back focal length Bf = 47.83                                                   fa = 282.15                                                                    fb = 117.68                                                                    ______________________________________                                    

wherein, upon focusing being effected by movement of both said biconvex positive lens and said positive meniscus lens, d₈ is a variable space and d₈ =7.18 for a photographing magnification β=-1/40, and wherein, upon focusing being effected by movement of only said biconvex positive lens, d₈ and d₁₀ are variables spaces and d₈ =5.89 and d₁₀ =4.36 for β=-1/40, and wherein R represents the radius of curvature of each lens surface, d represents the spacing between adjacent lens surfaces, nd and νd represent the refractive index and Abbe number, respectively, of each lens, the subscript numbers represent the order from the object side, fa represents the focal length of the first to the third groups, and fb represents the focal length of the first group to the movable positive lens component.
 4. A Gauss type photographic lens comprising, in succession from the object side, a first group including a positive lens component, a second group including a positive lens and a negative lens and having a negative refractive power as a whole, a third group including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group including a movable positive lens component comprising a biconvex positive lens and a negative meniscus lens having its convex surface facing the image side, focusing being effected by movement along the optical axis of either both said biconvex positive lens and said negative meniscus lens or by movement of only said biconvex positive lens, and wherein numerical data are as follows:

    ______________________________________                                         Total focal length f = 100.0, F-number 2.2,                                    Angle of view 26°                                                       ______________________________________                                         R.sub.1 = 65.25                                                                          d.sub.1 = 5.5                                                                             nd.sub.1 = 1.7481                                                                           νd.sub.1 = 52.3                           R.sub.2 = 165.0                                                                          d.sub.2 = 0.13                                                       R.sub.3 = 37.25                                                                          d.sub.3 = 12.5                                                                            nd.sub.2 = 1.67025                                                                          νd.sub.2 = 57.5                           R.sub.4 = 625.0                                                                          d.sub.4 = 7.25                                                                            nd.sub.3 = 1.61293                                                                          νd.sub.3 = 36.9                           R.sub.5 = 23.125                                                                         d.sub.5 = 25.88                                                      R.sub.6 = -28.88                                                                         d.sub.6 = 1.63                                                                            nd.sub.4 = 1.75692                                                                          νd.sub.4 = 31.7                           R.sub.7 = 312.5                                                                          d.sub.7 = 8.38                                                                            nd.sub.5 = 1.744                                                                            νd.sub.5 = 44.9                           R.sub.8 = -39.19                                                                         d.sub.8 = 10.00                                                      R.sub.9 = 218.75                                                                         d.sub.9 = 6.88                                                                            nd.sub.6  = 1.79668                                                                         νd.sub.6 = 45.4                           R.sub.10 = -68.75                                                                        d.sub.10 = 0.25                                                      R.sub.11 = -68.75                                                                        d.sub.11 = 1.88                                                                           nd.sub.7 = 1.79668                                                                          νd.sub.7 = 45.4                           R.sub.12 = -83.75                                                              Back focal length Bf = 47.25                                                   fa = 274.3                                                                     fb = 90.5                                                                      ______________________________________                                    

wherein, upon focusing being effected by movement of both said biconvex positive lens and said negative meniscus lens, d₈ is a variable space and d₈ =7.16 for a photographing magnification β=-1/40, and wherein, upon focusing being effected by movement of only said biconvex positive lens, d₈ and d₁₀ are variables spaces and d₈ =7.73 and d₁₀ =2.52 for β=-1/40, and wherein R represents the radius of curvature of each lens surface, d represents the spacing between adjacent lens surfaces, nd and νd represent the refractive index and Abbe number, respectively, of each lens, the subscript numbers represent the order from the object side, fa represents the focal length of the first to the third groups, and fb represents the focal length of the first group to the movable positive lens component.
 5. A Gauss type photographic lens comprising, in succession from the object side, a first group including a positive lens component, a second group including a positive lens and a negative lens and having a negative refractive power as a whole, a third group including a meniscus lens component comprising a negative lens and a positive lens cemented together and having its concave surface facing the object side, and a fourth group comprising a biconvex positive lens and a meniscus lens having its convex surface facing the image side, focusing being effected by movement along the optical axis of either both said biconvex positive lens and said meniscus lens or by movement of only said biconvex positive lens. 